R 16 Head Porting

[Gregs672000]

Steve has mentioned welding up the ports and recutting them the way he wants them, but knowing what to fill and where to cut would require a flow bench IMHO to get it right. Hogging out a runner without knowing how and where the head flows air is a real crap shoot. Might just end up reducing velocity.

[Daryl Smith]

"Hogging out a runner without knowing how and where the head flows air is a real crap shoot."
Good thing I don't recommend ANY 'hogging out'. Intake Ports are big enough on the R16 to support more power than most people are willing to spend to get there with supporting parts. Careful cleanup of the intake port will suffice.

Exhaust port is opposite. I see it as the Valve being too small, and the area around the guide as a choke point. No 'hogging' just careful, slow, deliberate, directed cutting. Once PAST the guide, the port opens up way bigger than it needs to be. I would like to shrink that about 20%. Will get into how when I narrow in on my options, but, welding is NOT on the menu for this head....

Welding on a head - Not that common, but it is done. Lots of threads/images to be found on the internet. Had combustion chambers welded on my old head...which is why I am now doing another head!! It was leaking through the combustion chamber into the coolant passages. Have been told the old Datsun heads are hard to weld......

Welding Example: http://performanceforums.com/forums/sho ... atsun-head

After studying this for a while and reading many articles and Vizards book, I think there is much improvement to be made by the home DIYer.
If you want it the best it can be right off the bat, send it to a reputable shop....If there is one near you that has time.
Could I make it worse than from the factory? Not likely, but, somebody might be able to....

[Daryl Smith]

"...knowing what to fill and where to cut would require a flow bench IMHO to get it right."

I don't think so. If you look at enough 'good' ports, and compare them to 'bad' ports, you start to see where the biggest problems lie. You will be able to tell a good port from a bad port, what makes a bad port 'bad', or a bad part of a 'good' port, and what needs to be done to correct the 'obvious' deficiencies. Not trying to make it perfect, just better, in some cases much better.

[JT68]

"I would like to shrink that about 20%."

That really isn't going to help_especially for a stroker engine. A waste of effort

"Could I make it worse than from the factory? Not likely, but, somebody might be able to...."

The Nissan engineers were quite adept at squeezing HP out of these little engines..Greg is correct yes, you certainly can make it worse.
There are all kinds of examples with many, many engines where well meaning folks dork up the ports and valves and make less power than the factory head. Chevy, Nissan, Ford- name a brand, this has been done.

I do agree that you need more exhaust flow and high exhaust velocity to maximize HP for either a race engine or a stroker, but work on the intake side is much more beneficial.

See the photo, Note these oversize seats- just about totally max'ed. Note how the 33mm ex valve does not occlude the seat- yes, you could use 34's, but it would decrease exhaust velocity and obstruct the outlet flow as it heads for the seat. 33 is an excellent size for the R head with improved seats.

image1(7).jpeg

[Gregs672000]

And Daryl, just so you know my friend, I know YOU would never hog out a port... I've read enough of your posts to know that you take things a step at a time in a methodical manner. Heck, I might not be running a megajolt if it weren't for you! Just warnings to others. But again, while one can look at ports and compare them, nothing replaces objective data. For example, I've discussed having a header made for my engine, thinking that I could just copy what's been done and gain more power. Now, I know you have researched this a lot. What Steve has told me is that there is just is no way to KNOW what the final outcome of such n such header design or runner length or size will do on a particular engine with different cams, compression ratio, head flow, etc until it's actually run on the dyno. There's theory, then there's real world application. Theory guides you, a dyno tells you (or crushes you... I've gone backwards before). I always encourage what you're doing Daryl, understand the drive and desire, and respect the research and work done. Without this kind of effort, nothing gets changed or improved. I certainly could not drive my engine on the street as safely as I do if you had not encouraged me to do the megajolt and provided parts and info. Keep experimenting and learning, then share it with us!

[Daryl Smith]

Hmmm...Well then.

I refuse to be a purveyor of the 'secret squirrel' BS that you need a professional to do ANY porting. VERY good gains can be made by almost any COMPETENT DIYer who bothers to do a little research and puts some thought into what they are doing. YES, a professional could squeeze several more CFM from the head, make adjustments for more 'swirl' and 'mixture motion', but, good gains are to be had without that expense or headache of finding a good 'professional', which I am not trying to discourage in any way, they are out there.

Greg,
Lot's of science and testing over the years has gone into headers. No, you cannot spec out your engine and build a max effort header spot on without testing. But, you can get it close, and make adjustments on the dyno to collector length. (And likely better than off the shelf units)
Also, thankyou for the vote of confidence.

Jim,
Nissan engineers haven't made any changes to these heads in 53+ years (I beleive the 1500 heads are basically the same casting?). Yes, they did an admirable job, for that time. Things have changed. Understanding has changed.

Reducing the size of the exhaust port - especially for a stroker - is a waste of time? Have you tried it? What are you basing this on? Have you sectioned a port to compare volume at the different points?

Everything I've read states a direct relationship between intake airflow and horsepower. For a 4 cyl that is 1 cfm @ 28" H2o to 1 horsepower. A STOCK intake port flows around 165 cfm @ .500" lift, actually very good. Anyone know a stock R16 head making 165 hp?? No? Well, it is, in my mind, because the exhaust will not flow enough.
I believe you could get just as much gain with a well thought out and thorough exhaust porting job and just a good cleanup of the intake, than spending a ton of time on the intake and little to no work on the exhaust. jmo
Valve sizes -
Intake - Every hotrodder will tell you to put the biggest intake valve that you can fit. That typically works out to about 50% of bore, give or take. Stock is @ 48%, not bad...
Exhaust valve - in the compression range for most street cars - according to the automotive brains, should be around 40% of the bore. So, with this in mind, the stock R16 exhaust valve, at 32 mm (37%) is already 3 mm undersized!! Compromises are made on the exhaust valve size, typically when increasing the compression ratio beyond what is normal for the street, as I understand it, a higher compression (13:1+) ratio will have a much stronger 'blowdown' and can get away with a smaller valve....a calculated compromise.

[JT68]

Daryl, If you think you are going to see large HP gains by adding port restriction, have at it, but as an engineer I'd estimate you are off the mark. IMHO.

I totally agree you can pick up a few HP by increasing the exhaust valve size, but because the exhaust is discharged under pressure, and flow increases by radius to the 4th power, you don't need to make particularly big diameter changes to make a significant increase in flow. Careful, expert seat work IS required however.

Since the intake charge is only moved in by one atm of pressure (non-turbo) you have to do more on the intake side to afford a significant change. That's why money spent there provides better yield.

Actually the 1600 head was improved over the 15., but of course Nissan hasn't changed the head lately. The physics hasn't changed either.

[GeoffM]

Hey Daryl,
Have you calculated the exhaust exit port size area as a % of valve area? Is this where you are going with the runner port mods? Trying to get to a certain % ratio for exit velocity?

[JT68]

Most of us have seen the videos of smashing & crushing the header pipes on the dyno making minimal changes to engine output. What that actually proves is that the header primary tubes are NOT the limiting factor for power output. I bring this up because the restriction and limitation is further upstream-It's the valve and seat area and the shrouded portion of the valves. The reality is during actual operation,the valve is not flowing anywhere close to uniformly around its' entire diameter (the shrouding really profoundly affects that). It's the valve& seat geometry that is primarily restricting flow-not the port design or primary header tube size. Since the seat/valve is not flowing even close to the theoretical max of the exhaust ports or primary tubes, the seat/valve combination is the limiting factor and where one should focus. IMHO

[Daryl Smith]

The picture below shows a couple of slices off the port mold I made....
Left side is as it exits the head, Right side is just after the valve guide. I don't think this is the smallest part of the port....

Exhaust Port CSA.jpg

Now....Tell me where I will be causing a restriction if I reduce the port size on the latter ~2/3 of the port past the restriction around the guide.
To be clear, for a given power output, there is an optimum size for the port. That is the CSA I am targeting. Too big you lose velocity, too small you choke it off.

It is also my understanding that because the exhaust is under much more pressure when the valve opens, that valve shrouding is much less of an issue.
Consider about 100 psi exhaust pushing out, vs 14.7 psi atmospheric pushing in. Yes you are going to have to work harder on the intake to get similar results for airflow, BUT, the intake ALREADY flows well, with a bit of cleanup and seat work it's great. The exhaust starts out with about a 30 cfm deficit from where it should be to be able to flow out what the intake is capable of flowing in. It NEEDS work!

[JT68]

Daryl,I don't disagree that the port is larger than needed. We've certainly agreed about that before. What I was tryin to communicate is that the port isn't the main restriction, so trying to make the port smaller isn't really going to do very much for you -certainly nothing remarkable.

"It's the valve, shrouding & seat geometry that is primarily restricting flow-not the port design or primary header tube size."

So what you are showing is fine, it just isn't very important to the big picture. You would be much better off spending more time on the intake side and optimizing every cam&intake parameter.

Just saying spending time and money making the port smaller isn't going to ADD significant power, which I think is what you are trying to do.
If you are trying to add low end, you are correct, find a 1500 head and go to 1-1.25" header primaries.

You asked earlier if I had ever decreased the port size...so how do I know? No I have not. I've never run 28mm Mikuni chokes on a U20 either, but I can tell you it isn't going to add HP. Just trying to help you out.

If we extrapolate your reasoning to the U20, then the Nissan engineers REALLY, really blew it with the U20 head and we should reduce the exhaust port size of all the U heads. I don't think that is desirable or necessary either. Nissan really did an amazing job upgrading to the U, so I think they actually had a pretty good handle on it.

[Mike Unger]

I'm not sure what the overall goal or intent is to this discussion but I can tell you that adding material to the ports is and has always been illegal in SCCA production car racing. This is why you're not going to find much about it. If this is for a street car and not for racing and a rules set then I would just add displacement, a different engine or some other more cost affective method to gain power and especial torque. Regarding flow, that alone from a flow bench is not a good measure of power output for these engines. How that flow induces swirl to the mixture and helps scavenging is more important in my opinion and experience. A head with great flow numbers may not make the best power. Looking at the deposits in a cylinder head after it's run can tell you a lot about how things are burning. IF I was going to add material to the port I would increase the bottom radius of the exhaust port and increase the radius above to make a larger overall bend in the exhaust port. I do this to some extent when I port Datsun heads but I make the port larger as I can't add material and my engines run at high rpms. More attention should be placed in the combustion chamber to enshroud the valves and then tuliping the port above the valve to help the venturi effect and the transition to the seat. Porting should be done with bias towards one side of the port to help induce swirl and contribute to scavenging especially as you increase overlap in the cam. All the this is lots of work and time for a street car when other options are available IMO.

[Gregs672000]

One of the things I love about you Daryl is that you are always doing things to learn about and then improve your engine. I share that drive. Sometimes I win, sometimes I lose (or screw up... Having to get a new block as we speak! Doh!). Experiments like this is how information is developed. You will always find folks who have varying degrees of experience, and ultimately one has to decide if they trust the knowledge or want to dig into it further to prove it one way or the other. Steve echoed what Mike said above, in that flow numbers are only a set of data from which to extrapolate what the engine might do, but there are many factors in a dynamic system that can throw expectations under the bus. He also cringes when talking about articles in typical hot rod mags (not suggesting that's your source for info!). Steve started porting heads at age 16, and he's gotta be near 60 now. He's tried damn near everything as he is the same kind of guy you are; hands on. He's worked and experimented his way through all restrictions, theories and evaluated what works and to what degree so as to best advise his customers on where to spend their money, from street goof balls like me to full race vintage Ferraris where everything counts and money is not an issue. Will my big valve head, that flows big numbers, produce the gains we're expecting? Hard to say yet, as things like cam lift/duration and timing, ignition mapping, air/fuel mix, manifold restrictions etc will all play a role on the dyno (where it matters). Were the larger valves critical or "the thing" that woke this engine Up? Probably not, but it was the next step to play with since the head was already modified in ways that were the most bang for the buck (Steve knows I have a budget). I think this is what JT is saying: From his experience these are the typical areas that will, when addressed, provide the most improvement for the effort made, which is a good way to do business and satisfy customer expectations. Can you gain more? Possibly, but it will take the kind of experimenting and effort you're doing, so your approach and goals will be a bit different. Welding in more material is a lot harder than grinding some out! And knowing how much to add and where is your best, educated guess, but one won't KNOW until she's on the dyno, and all other factors previously discussed will have to be addressed and adjusted to the new flow... but that's what makes this fun! (Fun for some!). I have no doubt that my engine has not reached its potential yet, but I don't think the head is the limiting factor... it's more about cam timing, ignition mapping and proper air/fuel ratios. It's hard to know what mods will work best on MY engine vs say Will's... with my compression, cam and ignition this head might work great for me, but strapped to Will's engine and cam it might be worse. Should I run 37mm chokes in my carbs or go larger to the 40s I have? What impact may that have on velocity with the larger valves? Will I create more peek power but sacrifice street driveability? One can only guess and test.
Clearly, this is not particularly technically helpful. I encourage you to continue your experiments and efforts... I love it! Take advice as you do, but do whatever YOU want to make changes and improve things, or not, and share the info with us. I'm hoping that nobody's ego is wrapped up in this and we're just exchanging info and experience... again, that's what makes this fun! I appreciate you and all the others who share info on this list!

[cktrap]

" I appreciate you and all the others who share info on this list!"
+1

[Daryl Smith]

"I don't disagree that the port is larger than needed. We've certainly agreed about that before. What I was tryin to communicate is that the port isn't the main restriction, so trying to make the port smaller isn't really going to do very much for you -certainly nothing remarkable."

Actually, the whole point of this excercise is NOT to make the WHOLE port smaller. It is to make the latter part of the port the "right" size and "shape" the port around the valve and guide so that it flows better at that point, which should make the port more uniform in size, flowing both more air, and at a higher velocity. Efforts will be made for port bias, to try to induce more swirl in the incoming mixture. A better flowing exhaust port also requires less overlap, which also means less reversion....

"It's the valve, shrouding & seat geometry that is primarily restricting flow-not the port design or primary header tube size."
I will be addressing the valve, seat geometry, and shrouding. Along with the port restrictions, and oversize sections.

"So what you are showing is fine, it just isn't very important to the big picture. You would be much better off spending more time on the intake side and optimizing every cam&intake parameter."
I am spending time on the intake, cleaning up and shaping the port a little, oversize valves, good performance 3+ angle seats, cam lift and duration targeted to my compression, rpm, and horsepower goals.

"Just saying spending time and money making the port smaller isn't going to ADD significant power, which I think is what you are trying to do."
No worries, mate. It ain't your time or money. Add "significant" power? Now that is the REAL question here isn't it!! My time, my experiment. Fact is with everything else I am modding up, there will be no way to tell how much, or IF it helps. However, I am going with the published books and automotive math to give the best chance at reaching and surpassing the goals I have in mind. All the little improvements add up, whether they are considered cost effective or not...

"If you are trying to add low end, you are correct, find a 1500 head and go to 1-1.25" header primaries."
Now that's just silly. You know very well an 1 1/4" primary header will never support the 160 - 170 hp I'm targeting. Likely would have good low end torque, but max out at 3500-4000 rpm on a 2L...roughly...

"You asked earlier if I had ever decreased the port size...so how do I know? No I have not. I've never run 28mm Mikuni chokes on a U20 either, but I can tell you it isn't going to add HP. Just trying to help you out."
Now that is just a very poor analogy and likely some narrow minded thinking. It's also definitely NOT trying to help.

"If we extrapolate your reasoning to the U20, then the Nissan engineers REALLY, really blew it with the U20 head and we should reduce the exhaust port size of all the U heads. I don't think that is desirable or necessary either. Nissan really did an amazing job upgrading to the U, so I think they actually had a pretty good handle on it."
Ok...extrapolate my reasoning.....the R head was used on a 1595 cc engine in a very mild application on a sports car, derived from even milder engines in .....trucks? The point of this thread is to improve the flow of this head for a 2+ litre engine that is not quite so mild. The U20 engine is more of a race engine detuned for a sports car, and, well, wouldn't you know it, many have said, including Lou Mondello, that the U20 exhaust port ISN'T all that great!! It also has a 36mm exhaust valve to start with...about 41.3% of bore diameter....and 3 mm larger than what you are saying is a good size for a 2L stroker engine.....
I'm really not sure what you are talking about extrapolating my reasoning....